In order to form a desired circuit pattern on semiconductor devices, a lithography technique is used. According to the lithography technique, a pattern is transferred using an original pattern which is referred to as a “mask (reticle)”. Further, to manufacture a precise reticle, an electron beam pattern writing technique which has excellent resolution is used.
One method of an electron beam writing apparatus which performs electron beam pattern writing on a mask includes a variable-shaped beam method. According to the variable-shaped beam method, by forming desirable shape by causing a beam to pass through both an opening of a first shaping aperture plate and an opening of a second shaping aperture plate, a figure is written on a target object set on a movable stage by an electron beam controlled to be deflected by a deflector. One time of irradiation of an electron beam is referred to as “shot”.
During writing on a mask or stand-by for writing, a drift (or a beam drift) which causes a shift from an irradiation position of an electron beam from a desired position occurs in some cases. When, for example, a mask is irradiated by an electron beam, a reflected electron is produced. The produced reflected electron causes charge up by colliding against an optical system or a detector in an electron beam writing apparatus, and a undesired electric field is produced. Then, a trajectory of the electron beam deflected and irradiated toward a mask changes. Such charge up causes a drift of an electron beam.
When a drift amount of an electron beam exceeds an allowable range, precision to write a pattern deteriorates. Hence, drift diagnosis for monitoring the drift amount of the electron beam during writing is performed. Further, as a result of drift diagnosis, drift correction for correcting the drift according to the obtained drift amount is performed.
JP-A 2010-192666 discloses an electron beam pattern writing method of changing a time interval to execute drift correction, based on a change amount of an area density of an area to be written.